Remove hackish way of getting the url for browser testing

tools/testing/dart/test_suite.dart

Index: tools/testing/dart/test_suite.dart
===================================================================
--- tools/testing/dart/test_suite.dart	(revision 23319)
+++ tools/testing/dart/test_suite.dart	(working copy)
@@ -997,6 +997,7 @@
                                                  subtestNames, subtestIndex);
 
         List<String> args = <String>[];
+
         if (TestUtils.usesWebDriver(runtime)) {
           args = [
               dartDir.append('tools/testing/run_selenium.py').toNativePath(),
@@ -1065,6 +1066,8 @@
         } else {
           multitestParentTest.addObserver(testCase);
         }
+        testCase.testingUrl = fullHtmlPath;
+
         doTest(testCase);
         subtestIndex++;
       } while(subtestIndex < subtestNames.length);